mysql/example/query_sync.cpp

//
// Copyright (c) 2019-2022 Ruben Perez Hidalgo (rubenperez038 at gmail dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//

//[example_query_sync
#include <boost/asio/ssl/context.hpp>
#include <boost/mysql.hpp>
#include <boost/asio/io_context.hpp>
#include <boost/system/system_error.hpp>
#include <iostream>

#define ASSERT(expr) \
    if (!(expr)) \
    { \
        std::cerr << "Assertion failed: " #expr << std::endl; \
        exit(1); \
    }

/**
 * Prints an employee to std::cout. An employee here is a boost::mysql::row,
 * which represents a row returned by a SQL query. You can access the values in
 * the row using row::values(), which returns a vector of boost::mysql::value.
 *
 * boost::mysql::value is a variant-like type representing 
 * a single value returned by MySQL.
 *
 * row::values() has the same number of elements as fields are in the SQL query,
 * and in the same order.
 */
void print_employee(const boost::mysql::row& employee)
{
    std::cout << "Employee '"
              << employee.values()[0] << " "                   // first_name (type boost::string_view)
              << employee.values()[1] << "' earns "            // last_name  (type boost::string_view)
              << employee.values()[2] << " dollars yearly\n";  // salary     (type double)
}

void main_impl(int argc, char** argv)
{
    if (argc != 4)
    {
        std::cerr << "Usage: " << argv[0] << " <username> <password> <server-hostname>\n";
        exit(1);
    }

    // The I/O context to perform all operations.
    boost::asio::io_context ctx;

    /**
     * Connection parameters that tell us how to connect to the MySQL server:
     * database credentials and schema to use.
     */
    boost::mysql::connection_params params (
        argv[1],               // username
        argv[2],               // password
        "boost_mysql_examples" // database to use; leave empty or omit the parameter for no database
    );

    /* We will use SSL in all our examples. To enable SSL, use boost::mysql::tcp_ssl_connection.
     * MySQL 8+ default is to use an authentication method that requires SSL, so we encourage
     * you to use SSL connections if you can.
     */
    boost::asio::ssl::context ssl_ctx (boost::asio::ssl::context::tls_client);

    // Represents a single connection over TCP to a MySQL server.
    boost::mysql::tcp_ssl_connection conn (ctx, ssl_ctx);

    // To establish the connection, we need a TCP endpoint. We have a hostname,
    // so we need to perform hostname resolution. We create a resolver for this.
    boost::asio::ip::tcp::resolver resolver (ctx.get_executor());

    // Invoke the resolver's appropriate function to perform the resolution.
    const char* hostname = argv[3];
    auto endpoints = resolver.resolve(hostname, boost::mysql::default_port_string);

    /**
     * Before using the connection, we have to connect to the server by:
     *    - Establishing the TCP-level session.
     *    - Authenticating to the MySQL server. The SSL handshake is performed as part of this.
     * connection::connect takes care of both.
     */
    conn.connect(*endpoints.begin(), params);

    /**
     * To issue a SQL query to the database server, use tcp_ssl_connection::query, which takes
     * the SQL to be executed as parameter and returns a resultset object.
     *
     * Resultset objects represent the result of a query, in tabular format.
     * They hold metadata describing the fields the resultset holds (in this case, first_name,
     * last_name and salary). To get the actual data, use read_one, read_many or read_all.
     * We will use read_all, which returns all the received rows as a std::vector.
     *
     * We will get all employees working for 'High Growth Startup'.
     */
    const char* sql = "SELECT first_name, last_name, salary FROM employee WHERE company_id = 'HGS'";
    boost::mysql::tcp_ssl_resultset result = conn.query(sql);

    // Get all the rows in the resultset
    std::vector<boost::mysql::row> employees = result.read_all();
    for (const auto& employee: employees)
    {
        print_employee(employee);
    }

    // We can issue any SQL statement, not only SELECTs. In this case, the returned
    // resultset will have no fields and no rows
    sql = "UPDATE employee SET salary = 10000 WHERE first_name = 'Underpaid'";
    result = conn.query(sql);
    ASSERT(result.fields().size() == 0); // fields() returns a vector containing metadata about the query fields

    // Check we have updated our poor intern salary
    result = conn.query("SELECT salary FROM employee WHERE first_name = 'Underpaid'");
    auto rows = result.read_all();
    ASSERT(rows.size() == 1);
    double salary = rows[0].values()[0].get<double>();
    ASSERT(salary == 10000);

    // Close the connection. This notifies the MySQL we want to log out
    // and then closes the underlying socket. This operation implies a network
    // transfer and thus can fail
    conn.close();
}

int main(int argc, char** argv)
{
    try
    {
        main_impl(argc, argv);
    }
    catch (const boost::system::system_error& err)
    {
        std::cerr << "Error: " << err.what() << ", error code: " << err.code() << std::endl;
        return 1;
    }
    catch (const std::exception& err)
    {
        std::cerr << "Error: " << err.what() << std::endl;
        return 1;
    }
}

//]